X-rays widely used for medical, industrial, and research purposes can be generated, for example, when high-energy electrons collide with a metal target. The electron source used to generate X-rays includes a thermionic source that induces electron emission by heating a metallic material and a field emission electron source that uses a nanomaterial.
The thermionic source has such disadvantages as a relatively short life span and difficulties in miniaturization, controlling the intensity of X-rays, and integration of a device.
On the other hand, the field emission electron source that uses a nanomaterial has such advantages that it is possible to have various electrical and physical forms and to generate X-rays at a higher power than those of a thermionic source, and it is easy to control the intensity of X-rays and to achieve integration and miniaturization of a device.
One example of such a field emission electron source is an X-ray emitting device in the form of a tube, which can be easily miniaturized. X-ray emitting devices are widely used in the fields of industrial systems for inspecting defects and quality, medical brachytherapy, 3D digital diagnostic imaging systems, and the like.
Meanwhile, a schematic structure on a vertical cross-section of a typical X-ray emitting device in a tube form is shown in FIG. 1. Referring to FIG. 1, the schematic structure and operation principle of an X-ray emitting device will be described.
The X-ray emitting device (1) may comprise an emitter (4) for emitting electrons when a voltage is applied, an anode (5) for emitting X-rays when the electrons emitted from the emitter (4) collide therewith, a tube (2) for providing an electron transfer path between the emitter (4) and the anode (5) and ensuring electrical insulation, and a focusing electrode (3) for focusing the electrons emitted from the emitter (4).
In the conventional X-ray emitting device (1), the tube (2) is made of glass, which is easy to process and hardly absorbs X-rays, and a ferronickel alloy is typically used for the focusing electrode (3).
As described above, in the conventional X-ray emitting device (1), the tube (2) and the focusing electrode (3) are made of different materials. Thus, in order to join them, a complicated process has been typically carried out in which the surfaces of the tube (2) and the focusing electrode (3) to be joined are subjected to metalizing treatment, followed by brazing (6) treatment.
The tube (2) and the focusing electrode (3) thus joined together form the body of the X-ray emitting device (1), and the inside thereof forms a communicating hollow, which serves as a closed electron transfer channel (c) in which electrons can move from the emitter (4) to the anode (5). The electron transfer channel (c) can be maintained in a vacuum.
However, the conventional X-ray emitting device (1) described above has a technical problem in terms of structural stability and difficulties in the manufacturing process.
Specifically, the tube (2) made of glass has low mechanical strength and may thus be easily broken. In addition, it is difficult, despite the metalizing and brazing (6) treatment, that glass and metal, which are different materials from each other, can be joined in such a desirable bonding state as not to be damaged by an external force and without deformation by the heat generated in the X-ray emitting device (1).
Further, due to the difference in thermal expansion coefficients between glass and metal, which are different materials from each other, relatively strong stress may be applied to the joining interface by the thermal shrinkage of the tube (2) and the focusing electrode (3). This may cause a problem that the joining state of the tube (2) and the focusing electrode (3) may be damaged or deformed when the X-ray emitting device (1) is used repeatedly or for a long period of time.
For this reason, the conventional X-ray emitting device (1) is not excellent in durability. In particular, the sealing state of the electron transfer channel (c) may be impaired by the damage or deformation of the bonding state, which may lead to a problem that the degree of vacuum is deteriorated.
In terms of the difficulties of the manufacturing process, the metalizing and brazing (6) treatment is a process with a significantly high degree of difficulty and precision. Thus, it is difficult to manufacture the conventional X-ray emitting device. In particular, when it is miniaturized, the defect rate is high. In another aspect, the metalizing and brazing (6) treatment requires skilled manpower and the cost is high as well, which may raise the price of the X-ray emitting device (1).
Accordingly, there is a demand for a novel X-ray emitting device, which addresses the technical problems described above.